Crystalline oxide thin films on Si have attracted considerable attention in recent years since the unique properties of those oxide materials can be combined with Si-based integrated circuits. For instance, STO is now considered as a high dielectric constant oxide to replace SiO2 as a gate oxide in metal-oxide-semiconductor devices. On the other hand, STO is a cubic perovskite structure and has a lattice constant of 0.3905 nm, which is closely matched to a large number of other perovskite oxides. Thus, the STO/Si system can be used as a growth substrate for fabrication of thin films of other functional oxides and carbon nanotube transistors.
The quite large lattice mismatch between STO and Si ((aSTO−aSi)/aSi×100%=28%) presents a challenge for epitaxial growth. Additionally, the formation of an amorphous oxide over Si surface may prevent STO film from crystal growth. Previous attempts to obtain high-quality STO thin films grown directly on Si have been unsuccessful, These STO films grown directly on Si using various deposition techniques were usually polycrystalline with randomly oriented grains. In the case of STO thin films by pulsed laser deposition (PLD), the co-existance of two peaks of (hh0) and (h00) was always observed.
It is known that randomly oriented polycrystalline films have certain limitations in various applications. Formation of various grain sizes and growth orientations and co-existence of secondary phase may cause low performance of the integrated devices. Consequently, it is commonly believed that the use of appropriate buffer layers between STO and Si substrate is required for the highly oriented growth, especially for the epitaxial growth of STO thin films. McKee et al. demonstrated the epitaxial growth of STO on Si (001) with a SrSi2 submonolayer interface by molecular beam epitaxy (MBE) technique, Extensive research has been carried out on the growth of STO on Si (001) with various single buffer layers and/or multi-buffer layers. In this invention, we firstly develop a method to prepare STO films with single (110) orientation grown directly on differently oriented silicon substrates by PLD technique. Epitaxial STO (110) films have been grown successfully on Si (100) without any buffer layer.